The problem of restricting access to a particular item to one or more authorized users has existed for centuries, and over this time, a number of methods have been developed for securing an item of interest from unauthorized users. The most widely used approach is the use of mechanical or electronic locks that can be released via a key or key card. A drawback of relying on keys and key cards to establish a user's identity is the necessity for a user to carry an object at any time in which the item of interest must be accessed, making it more difficult to access the secured item on demand. Many computer systems and financial accounts utilize passwords or PIN (Personal Identification Number) to authenticate a user, but these systems are subject to the vagaries of human memory and can be compromised through a number of means, including brute force decryption attacks, malware keyloggers hidden in a computer system, the selection of a trivial or weak password or PIN by a user, and social engineering. More secure systems may utilizing biometric approaches to authenticating a user, such as scanning a thumbprint, but effective biometric systems tend to be costly to implement, and so far, these systems have not been widely adopted.